Broadband Wireless Access. The Essential Guide for Wireless ISPs

Transcription

1 Broadband Wireless Access The Essential Guide for Wireless ISPs

2 Legal Rights Legal Rights Copyright 2003 Netronics Inc. All rights reserved. The material contained herein is proprietary, privileged, and confidential. No disclosure thereof shall be made to third parties without the express written permission of Netronics Inc. Netronics Inc. serves the right to alter the equipment specifications and descriptions in this publication without prior notice. No part of this publication shall be deemed to be part of any contract or warranty unless specifically incorporated by reference into such contract or warrant. Statement of Conditions The information contained in this guide is subject to change without notice Netronics Inc. shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this guide.

13 Chapter 1 - Introduction This document is aimed to satisfy the needs of the Internet Service Providers industry for comprehensive information on Broadband Wireless Access (BWA). It is intended for ISPs who are looking at BWA as an alternative to traditional wire- or cable-based services, including: a. An established ISP that considers adding BWA to its infrastructure for one or more of the following reasons: Expand coverage to new customers-either in an already served area or in new areas. Provide services in rural and other areas where wireless access is the only viable option. Enhance its services portfolio to improve competitive position and increase revenues and profits. Eliminate expenses, delays and long-term commitments associated with getting access services from a third party. b. A new entrant to the rapidly evolving ISP market place wishing to benefit from the advantages of a business based on BWA. Regardless of the reasons for becoming interested in BWA, there are numerous questions that must be answered, related to various crucial issues that must be considered prior to taking the decision to invest in a BWA based network, while launching a new BWA network and throughout the life time of the network. We at Netronics have been working closely with global telecom and Internet operators over a long period of time. A wide range of professionals in Netronics senior management, sales force, customer service and technical staff have met a long list of Operators management, operations and technical teams. They have discussed challenges together, made errors together, fixed problems together and succeeded together. Netronics professionals have gathered years of experience and know-how, witnessing Operators experiences, preferences, challenges and difficulties concerning many facets of their overall network. Our staff has accumulated a large set of testimonials regarding our partners network build-out. What they saw related to various aspects of the network and to various types of networks. Over time, we witnessed a wide range of situations experienced by our partners: from the management decision-making process to technical and logistic activities by different types of operators: cellular, data access, ISPs and local independent telcos. 1-2 Essential Guide to Wireless ISPs

14 Introduction Until now, this valuable information has not been shared in any integrated, comprehensive format. Moreover, we began to notice that different operators often faced identical challenges. Unaware of their predecessors experience, they often repeated the same mistakes. In the meantime, a number of Netronics employees have, over time, witnessed a recurrence of questions and problems among our many customers. The questions may be directly related to the Netronics solution, or may be directed to overall network challenges. We have assembled all the information gathered from the field into a comprehensive format that shows the big picture while recalling the small details. This overview refers to all the aspects concerning a BWA project, from backbone interfaces, to integrated network solutions at the customer site; from the NAT location debate to management system considerations; from VoIP to billing; it discusses technology pros and cons as well as business models. This document offers you a comprehensive overview of our accumulated knowledge in order to help you understand all the important aspects of BWA and assess the project you are taking or about to take. The document has been divided by subject matter, so that you can skip to read only the areas that are relevant to you, or read its entirety - whichever fits you best. We urge you to look for more information on specific issues in other sources available through your Netronics representative. We also invite you browse our material-wealthy website at It must be emphasized that many applicable issues vary significantly among countries and even regions. These includes issues such as local regulations that affect technical considerations and issues that affect the business model such as the competitive landscape, labor costs, customers profile etc. You are invited to consult with our experts in order to reach the right conclusions and build the business plan that takes into account all the unique aspects of becoming a Wireless ISP in your target area. 1-3

17 Chapter 2 - Wireless Access Systems Basics Licensed and Unlicensed Frequencies When discussing wireless solutions, it is important to distinguish between frequencies that are licensed by the local radio regulatory agency and those that are not. By unlicensed services, we refer to those transmitting devices that must meet certain defined equipment tolerances, but that are otherwise unrestricted in their deployment. Actual systems that employ such equipment are considered unlicensed because prior regulatory authorization and licensing requirements of these systems are unnecessary. Local applicable regulations, such as Part 15 of the FCC Rules, establish equipment tolerances for transmitting devices that are considered unlicensed. The applicable regulations, such as FCC Part 18, cover frequency bands of certain industrial, scientific and medical (ISM) equipment that can also be used in an unlicensed manner. Certain of the ISM frequency bands (including 2.4 and 5.8 GHz) are available for use by commercial entities. Such unlicensed facilities have relatively low power and small coverage footprints. In addition, because these systems are unlicensed, they are not protected from interference. Such interference can become extreme in areas where multiple unlicensed systems that use the same frequency spectrum are installed. Typically, smaller and medium-size service providers use unlicensed frequencies. While an unlicensed frequency can meet the needs of many people, it is not always appropriate as a broad solution. A primary concern is that there is no control over the number of devices that share an unlicensed environment. Devices that share these frequencies can be installed anywhere by anyone with no regulation and no recourse for interference. Thus, it may be very difficult for people to truly depend on this service for business or other important applications. Licensed frequencies provide the probability of more stability than unlicensed frequencies; A licensed frequency ensures the service provider that within a certain area he is the only one that is allowed to use the allocated frequencies. However, this stability comes at a high price. The government radio agencies auctions the limited number of licensed frequencies, and the price is far from being low. 2-2 Essential Guide to Wireless ISPs

18 Spread Spectrum Radio Technologies Spread Spectrum Radio Technologies A popular solution to the licensing problem is provided by the emergence of Spread Spectrum (SS) technology. This digital technology provides most of the capabilities and performance of a licensed radio system with a license-free approach. The term Spread Spectrum (SS) describes a communications technique whereby a radio frequency signal is modulated (spread) a second time so as to generate an expanded bandwidth wideband signal. Spread Spectrum is usually used for data transmission. The two most popular types of Spread Spectrum modes are Frequency Hopping and Direct Sequence. DSSS radios occupy a consistent piece of allocated spectrum constantly. FHSS radios don't always sit on the same exact frequency it seamlessly skips from band-to-band over a fixed portion of spectrum. FHSS is a transmission technology used in LAWN transmissions where the data signal is modulated with a narrowband carrier signal that "hops" in a random but predictable sequence from frequency to frequency as a function of time over a wide band of frequencies. The signal energy is spread in time domain rather than chopping each bit into small pieces in the frequency domain. This technique reduces interference because a signal from a narrowband system will only affect the spread spectrum signal if both are transmitting at the same frequency at the same time. If synchronized properly, a single logical channel is maintained. Direct Sequence SS also involves the application of pseudorandom codes known to both ends of the link, but the code is used to cause a fixed frequency transmitter to spread its power more or less evenly across a wide band of RF spectrum, usually many Megahertz. Pseudorandom codes are selected to give the spread signal a noise-like character, which when detected by a conventional receiving device, looks very much like random noise. The receiver must be wide enough to recover all of this bandwidth in order to recover the transmitted signal, and then, using the same pseudorandom code as the transmitter, de-spread the signal to its original data component. Direct Sequence systems also have good immunity to noise and interference when used with highly directional antennas in relatively short-range applications. 2-3

19 Chapter 2 - Wireless Access Systems Basics There is an ongoing debate about which spread spectrum technology is better. Both direct sequence and frequency hopping systems have advantages and disadvantages inherent to the equipment used. FHSS systems are capable of leaping past interference, but at the price of delayed data flow. DSSS technology allows you to program past sources of interference, so the user does not experience delays. However, interference can change and you have to re-program around it again in order to maintain speed. A newer technology, made available through advance in DSP technologies, is OFDM (Orthogonal Frequency Division Multiplexing), an FDM modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of cross-talk in signal transmissions. OFDM is robust in adverse channel conditions and allows non line of sight operation while maintaining a high level of spectral efficiency. It effectively mitigates performance degradations due to multipath and is capable of combating deep fades in part of the spectrum. The use of Orthogonal Frequency Division Multiple Access (OFDMA) allows simultaneous transmission from several users, with only a fraction of the sub-carriers assigned to each user. In this way the benefits of large FFT size are combined with the granularity advantage of small FFT size. An additional advantage of OFDMA is an improved upstream link budget, due to smaller effective bandwidth of each user. Industry Standards and Organizations IEEE Many of the BWA solutions are based on the IEEE Wireless LAN standard. Usually, Wireless LAN gear provides an indoor coverage radius of about 200 meter. However, both manufacturers and service providers have learned how to get more out of IEEE based equipment, in order to make it do things it was not originally designed to do. With proper thought, research, and RF engineering principles applied to these simple Wireless LAN devices, customers as far as 30 km away from your antenna have a chance to connect to get broadband access services. 2-4 Essential Guide to Wireless ISPs

20 Industry Standards and Organizations IEEE , the first internationally sanctioned standard for wireless LAN, was completed and published in The original standard defined data rates of 1Mbps and 2Mbps via radio waves using frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS). Specification a is a supplement to the standard, which defines a high-speed physical layer in the 5GHz band based on Orthogonal Frequency Division Multiplexing (OFDM) modulation, providing data communication capabilities of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps. (6, 12, and 24 Mbps mandatory). In 1999, the b amendment to the standard was ratified, adding higher speed of 5.5 and 11Mbps with DSSS. The Media Access Control (MAC) as defined by the standard is very similar in concept to the wired Ethernet MAC (802.3 standard), supporting multiple users on a shared medium. However, the protocol was modified for sharing access over the air taking into account the different characteristics of the wireless media, handling interference and other radio related problems and ensuring robustness and data integrity. IEEE IEEE WirelessMAN standard was designed specifically to solve the unique problem of the wireless metropolitan area network (MAN) environment and to deliver broadband access services to a wide range of customers. The IEEE Media Access Control (MAC) protocol was designed for point-to-multipoint broadband wireless access applications. It provides a very efficient use of the wireless spectrum and supports difficult user environments. The access and bandwidth allocation mechanisms accommodate hundreds of subscriber units per channel, with subscriber units that may support different services to multiple end users. To efficiently deliver a variety of services, the protocol supports both continuous and burst traffic. Through the WirelessMAN MAC, each base station allocates uplink and downlink bandwidth to satisfy, almost instantaneously, the prioritized bandwidth requirements of the subscribers. The MAC protocol controls the media so that Subscriber Units transmit only in allocated transmitting opportunities. The MAC protocol is designed to carry any data or multimedia traffic with highly flexible Quality of Service (QoS) support. The connection-oriented protocol allows flexible QoS attributes definition for each connection. 2-5

21 Chapter 2 - Wireless Access Systems Basics WiMAX IEEE a amendment to the standard supports the 2 11 GHz band including licensed and license-exempt spectrum, offering the opportunity to reach many more customers (at lower data rates) less expensively, thus to provide cost-effective services to individual homes and SMEs. The GHz physical layer assumes line-of-sight propagation and uses single-carrier modulation. Downlink access is TDM-based, with individual stations allocated time slots serially. Uplink access is TDMAbased (Time Division Multiple Access). Both time division duplex (TDD), in which the uplink and downlink share a channel but do not transmit simultaneously, and frequency-division duplex (FDD), in which the uplink and downlink operate on separate channels, are supported. Adaptive burst profiles are supported, where modulation and coding options may be dynamically assigned on a burst-by-burst basis. The 2 11 GHz physical layer design is driven by the need for non-lineof-sight (NLOS) operation, with significant multipath propagation, as expected in residential applications. Air interfaces supported are singlecarrier, orthogonal frequency-division multiplexing (OFDM) with TDMA access and orthogonal frequency-division multiple access (OFDMA) where multiple access is provided by addressing a subset of the multiple carriers to individual receivers. WiMAX is a non-profit industry trade organization formed by leading communications component and equipment companies to promote and certify compatibility and interoperability of broadband wireless access equipment that conforms to the IEEE* and ETSI* HIPERMAN standards. WiMAX promotes a new standard for last-mile wireless technologies designed to provide broadband connectivity to homes, businesses and Wi-Fi HotSpots, competing with today s wireline DSL, cable, and T1 broadband access systems. Until now, the uptake of BWA technologies has been restrained by the lack of interoperability between the equipment of the industry s many manufacturers and the availability of standards-based, volume components. Led by the initiative of leading Wi-Fi and BWA component suppliers like Intel and Netronics, interoperable WiMAX-Certified systems built upon standards-based silicon will help broadband wireless access to achieve its full massmarket potential as a price-competitive and flexible alternative to wired broadband solutions. 2-6 Essential Guide to Wireless ISPs

22 Industry Standards and Organizations WiMAX will accelerate and increase the success of future interoperability by providing tools for conformance testing now. Tools can be used during the equipment maker's system development process today to ensure conformance with the current standards-based product roadmap as it evolves. Netronics has signed a strategic agreement with Intel to work together to incorporate Intel s pioneering a chips into the company s coming line of next generation, interoperable Broadband Wireless Access (BWA) systems. Working in close cooperation, Netronics is now developing next generation products based on Intel s chips with the intention of being one of the first to launch a WiMAX-Certified system. 2-7

25 Chapter 3 - Wireless Access System Architectures Sectorized Cellular Architecture The primary architecture for deploying wireless broadband access is a sectorized cellular model. The basic geographic unit of a cellular system is the cell. Cells are base stations transmitting over small geographic areas that are represented as hexagons. The term cellular comes from the honeycomb shape of the areas into which a coverage region is divided. Each cell size varies depending on the landscape. Because of constraints imposed by natural terrain and man-made structures, the true shape of cells is not a perfect hexagon. To increase capacity and enable a better utilization of the available frequencies, directional antennas are used to provide several sectors within each cell. Unlike in an omni-directional antenna, where power radiates equally in all directions in the horizontal (azimuth) plane, a directional antenna concentrates the power within a desired geographical area in certain directions. The radiative properties of these antennas are described by a radiation pattern, which is a plot of the radiated energy from an antenna measured at various angles at a constant distance from the antenna in a particular plane. Typically, the plot is presented in the pictorial form of a polar plot for a 360-degree angular pattern as illustrated Figure 3-1. The position of maximum radiated power, known as the bore-sight, is at the 0o. The radiation power is plotted against the angle with respect to the bore-sight direction. The plot consists of a main lobe (also referred to as front lobe), which contains the bore-sight, and several minor lobes including side and rear lobes. Between these lobes are directions in which little or no radiation occurs. These are termed nulls. Nulls may represent a 30 or more db reduction from the power at bore-sight (less than onethousandth the energy of the main beam) in transmitted signal level in that direction. The dotted circles in Figure 3-1 are used to indicate the magnitude of the radiation. The angle between the two points where the power is one-half the main lobe s peak value is known as the beam width of the antenna. Directional antennas have been deployed in the cellular networks to enhance the radio capacity. There are several different sectorization schemes, varying on the number of sectors or antennae, the beam width of the antenna, and the orientation of the bore-sight directions. 3-2 Essential Guide to Wireless ISPs

27 Chapter 3 - Wireless Access System Architectures In sectorized cellular architecture, each Base Station is comprised of several Access Units connected to directional antennas. Each Access Units serves customer in a specific sector, defined by the beam-width of the antenna. Sectorization also helps preventing unnecessary interference from other systems as well as from neighboring sectors, because they only transmit and receive radio signals in the specific direction defined by the characteristics of the antenna. Desired cell s structure depends on various factors, including topography of the area that should be served and distribution of customers in the area. In wireless broadband, RF is a critical asset and it should never be wasted or over deployed. Flexibility in selecting the number of Access Units in the base station and the antennas to be used is important for various reasons: a. Not all cells originate in the middle of the area needing coverage. For example, a tower may be on a ridgeline at the edge of town. In this case, no coverage may be needed for the side of the tower opposite the town. b. For areas with low customers density, a smaller number of Access Units using relatively wide sectors may be sufficient. In very dense areas narrower sectors will be needed, and in some cases two or three Access Units per sector may be needed to support the bandwidth demand. Netronics data shows that the average cell in U.S. markets is configured with three (3) 120 sectors with an 8 (eight) kilometers radius providing approximately 200 square kilometers of coverage (cell area = πr2). However, we have some customers with as many as eighteen (18) 60 antennas on a single tower where each sector is served by three (3) Access Units for increased capacity, and as little as one (1). Many cells in very flat areas achieve coverage of more than 700 square kilometers. Your configuration will depend on a variety of factors from customer density and availability, topography, and antenna height. The subsequent chapter on design will discuss in detail these important issues. 3-4 Essential Guide to Wireless ISPs

28 Micro-cellular Architecture Micro-cellular Architecture Occasionally, dense customer availability, limited access to highly placed antennas or other factors may lead to a decision to deploy a micro-cell. A micro-cell is generally regarded as a cell approximately 1.5 kilometers or less in radius. Such cells are usually deployed using omni antennas mounted at heights of 15 meter or lower. The environment may be dense enough such that even this small a cell can achieve full capacity. Often such cells are installed in a contiguous manner, such as linearly following city streets, installing the equipment on utility polls or roofs. This can dramatically alter the economics of wireless broadband deployments. Another excellent choice for micro-cellular deployment is for MDU (multi-dwelling unit) campus environments, such as sprawling garden style apartments, dormitory areas, and light industrial complex parks. Such a model seeks to take advantage of the high user density in these areas. Installation of the micro-cell base station equipment is generally far less expensive in terms of labor deployment and monthly lease costs compared to a typical tower. Users are typically so close to the base station that they may not need any exterior antenna. This permits a 100% RF model; no use of new or legacy wiring is required. This also greatly reduces truck roll costs and eliminates hassles over unsightly multiple antenna attachments. Cell Extension In many cases certain areas may not be reached due to obstacles or range limitations that inhibit deployment of a base station that can cover the area. The reach of a cell can be extended using a cell extender (also called a repeater) to provide coverage to areas that could not otherwise be served. In addition, cell extension can be used to serve small remote clusters of subscribers where subscriber density or other economic factors do not warrant a completely dedicated cell. Cell Extenders that operate in mixed radio bands offers additional benefits: Operators that typically provide services using the 2.4 GHz or 5 GHz band, can benefit from the advantage of operating locally in the 900 MHz band, being able to provide services to customers within a radius of half a mile in non line of sight environments with heavy foliage and other obstacles. 3-5

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